Glucose Tolerance Tests
Since the endocrine system affects the way the body metabolizes glucose, endocrinologists often order the glucose tolerance test. One of the most common forms of this test is the oral tolerance test. You must fast after midnight on the night before you go for the test. During the test, you will have to drink a liquid that contains a specific amount of glucose. A phlebotomist will draw your blood before the test to determine your glucose level before you drink the glucose solution. During the test, the phlebotomist will take more blood every 30 to 60 minutes.
The National Institutes of Health reports that normal glucose levels during this test are as follows:
Pre-test: 60 to 100 mg/dL
After one hour: less than 200 mg/dL
After two hours: less than 140 mg/dL
If your blood glucose is 140 to 200 mg/dL after two hours, you have an increased risk for diabetes. This is also known as pre-diabetes. Glucose levels of above 200 mg/dL after two hours indicate diabetes mellitus, or type 2 diabetes.
Risks of this test include fainting, bleeding, bruising, infection, and lightheadedness. Test results can be altered by several factors. These factors include vigorous exercise, stress from surgery, infection, and use of certain medications. Medications that alter the results of the glucose tolerance test include psychiatric medications, beta-blockers (used for high blood pressure and anxiety treatment), birth control pills, corticosteroids, and some diuretics.